In a conventional adjustable wrench, a movable jaw opposes a stationary jaw. The stationary jaw has a cavity which receives a shank of the movable jaw. The shank has teeth on a rearward edge which engage a worm gear mounted rotatably to the stationary jaw. Rotating the worm gear moves the movable drive face toward and away from the stationary drive face to adjust for the nut.
Adjustable wrenches commercially available require that the user tighten the movable jaw on the nut each time the wrench is placed on the nut. Then, to remove the wrench at the end of a stroke, the user normally has to loosen the movable jaw. The user has to retighten the wrench at the beginning of the next stroke. Also, often the worm gear will tend to loosen as the wrench is used. This makes using an adjustable wrench more time consuming than using a conventional fixed jaw wrench. Unless the user is careful, damage to the nut corners will occur due to failure to properly adjust the jaws each time.
U.S. Pat. No. 5,239,899 shows a positioner member which advances and retracts to engage one side of the nut. The positioner member maintains the nut in a desired central position relative to the jaws. The jaws are also curved or arcuate for improved driving. The positioner member is retained by a tongue and groove arrangement with the shank of the movable jaw. Advancing the movable drive face toward and away from the stationary drive face moves the positioner member forward and rearward. In one embodiment of the '899 patent, the stationary drive face is truncated to allow ratcheting action of the adjustable wrench relative to the nut.